In a packet switched network (PSN) (the term used in English), the data to be transmitted take the form of packets which are processed by the switching devices of the network until they reach their destination. The set of packets to be transmitted from a source to a destination forms a data stream.
An example of a method used in packet switched networks for routing data packets is MPLS (multiprotocol label switching). The purpose of the MPLS method is to add to the headers of data packets one or more labels containing information allowing the network switching devices to determine the next hop that a packet must complete in order to reach its destination. The MPLS method is detailed in a document published by the IETF (“Internet Engineering Task Force”, an Internet standardization team), reference RFC 3031 (where RFC signifies “Request For Comments”).
However, the MPLS can only be used to route packets conforming to the protocol known as IP (Internet Protocol).
In order to overcome this problem, the PWE3 (PseudoWire Emulation Edge to Edge) standardization team of the IETF has defined the concept of a “pseudowire” for the emulation of a point-to-point link between two devices, this link being based on a packet switched network using the IP/MPLS technology. Pseudowires of this kind, as defined in document RFC 3985, can be used to transmit data packets not conforming to the IP protocol, such as data packets conforming to the ATM protocol.
The document “Signaling Root-Initiated Point-to-Multipoint Pseudowires using LDP”, draftmartini-pwe3-p2mp-pw-01.txt, proposes a solution for providing a point-to-multipoint pseudowire from a root device to a plurality of terminating devices, called leaf devices, thereby forming a data distribution tree.
In this type of architecture, the traffic is distributed in the downstream direction, in other words from the root device to the set of leaf devices. The traffic in the upstream direction, in other words from one of the leaf devices toward the root device, flows through a separate point-to-point pseudowire established between this leaf device and the root device.
Thus it is necessary to establish a number of point-to-point pseudowires equal to the number of leaf devices, creating a harmful loss of bandwidth and entailing a high degree of complexity for the establishment and maintenance of the set of pseudowires.
In particular, since all the point-to-point pseudowires terminate on the root device, they have to be identified and controlled independently by the root device, which considerably complicates the control of this device. This is because it is necessary to configure each pseudowire individually, to maintain a signaling session with each leaf device for the maintenance of the pseudowires, to supervise individually each pseudowire established in this way, and so on. Moreover, controlling the volume of data to be aggregated at the root device is made more complicated.